The usual manner of making multi-stage enamelled dials consists in taking a metal plate of very small thickness, generally made of copper, a copper alloy or silver, forming a layer of enamel at the surface of the substrate by successive deposition and firing operations, said layer having a thickness generally comprised between 600 and 800 μm, and a layer of counter enamelling of smaller thickness on the back side of the plate. The counter enamelling has an essentially technical function countering the stresses that are created in the metal plate during successive firing operations. An aperture of the desired dimensions for the secondary dial is then cut, then the surface of an enamelled disc, produced in the same way, is machined and cut to the dimensions of the aperture possibly reducing the thickness of the enamel, and finally the disc is welded in the aperture, which produces a quite visible mark on the back of the dial and can damage the secondary dial. The method that has just been briefly described is very difficult to implement, has a significant discard rate and finally leads to a finished product with a very high cost.
In order to give an enamelled on metal dial more relief without having the drawbacks of the aforecited prior art, taking a thicker plate has also been proposed and machining hollows therein that are then covered with a sufficiently thick layer of enamel to conceal the metallic appearance of the bottom. The enamelled dial thereby obtained is significantly thicker, which causes an increase in the dimensions of the case, which then no longer answers current requirements for wristwatches.
Deforming a metal base plate has also been proposed, for example by stamping, and then carrying out the enamelling. The parts that have been deformed have altered thermal behaviour, such that the firing operations usually cause cracks in the enamel layers that lead to the manufacture part being discarded.